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Pancreatic Insufficiency
CF is the most common cause of exocrine pancreatic insufficiency in patients younger than 30 years (72). Pancreatic dysfunction results from the fundamental defect in epithelial chloride ion permeability, which is functionally linked to bicarbonate and water secretion. Inspissation of abnormally concentrated pancreatic juice produces proximal duct obstruction (1,82). Acinar atrophy and a mild inflammatory reaction result, followed by progressive fibrosis, fatty replacement, duct ectasia, cyst formation, and calcification (Figure 12). Malabsorption is exacerbated by an abnormally low duodenal pH, which impairs lipase activity and diminishes the bioavailability of enteric coated enzyme replacements (83). Greater than 90% of exocrine pancreatic function must be lost before clinical manifestations, which include failure to thrive, steatorrhea, fat intolerance, abdominal pain, bloating, and flatulence, are apparent (84). Nevertheless, pancreatic dysfunction is clinically apparent in 85%-90% of patients with CF (19). Because the ion transport defect of CF has not been localized to the islet cells of the pancreas, endocrine dysfunction is considered secondary to fibrosis and other unknown factors (1). Approximately 30%-50% of patients have glucose intolerance, and 1%-2% require insulin therapy (19,72). Clinical evidence of pancreatitis is unusual, despite histologic evidence of chronic inflammation in CF (1).
Plain radiography of the abdomen may demonstrate multiple punctate calcifications that conform in distribution to the location of the pancreas (Figure 13).
Sonographic abnormalities of the pancreas are reported in 70%-100% of patients with CF (85,86,87,88,89,90). The pancreas usually appears small and echogenic and may be inapparent (90). There is poor correlation between sonographic findings and pancreatic function (86,91).
The spectrum of CT findings parallels the varying degrees of fat replacement, fibrosis, calcification, and cyst formation (25,84,90,92). Early in the disease process, the pancreas may be heterogeneous with areas of fat attenuation interspersed with soft-tissue attenuation, but complete fatty replacement may occur in older patients (Figure 14).
The appearance of the pancreas in CF at magnetic resonance (MR) imaging depends on the amount of fat and fibrosis. With lipomatous change, increased signal intensity is seen on T1-weighted images. Areas of fibrosis have low signal intensity on both T1- and T2-weighted images. Meaningful pancreatic size assessment is hampered by the wide range of normal in the pediatric population and the poor definition of the fatty replaced pancreas from normal retroperitoneal fat (93,94). Complete fatty replacement of the pancreas correlates fairly well with advanced pancreatic disease, although patients may have normal MR imaging findings and still require enzyme replacement therapy (94).
Pancreatic Cystosis
Pancreatic cysts are relatively common in CF. The cysts are typically microscopic or small (1-3 mm in diameter) (Figure 15). Less commonly, scattered cysts up to several centimeters in diameter have been described. Rarely, aggregates of true epithelial-lined cysts completely replace the pancreas and may cause mass effect within the abdomen (Figure 16). This condition has been called pancreatic cystosis, which is thought to represent the extreme end of the spectrum of cystic changes secondary to ductal obstruction (95).
The radiologic features of this rare manifestation of CF were recently described in two patients (95). CT and US findings included complete replacement of the pancreas by a multiloculated cystic mass. The individual cysts ranged from 0.5 to 12 cm in diameter. The typical clinical setting and complete cystic transformation helped exclude other causes of a complex cystic pancreatic mass, including autosomal dominant polycystic kidney disease with pancreatic involvement, microcystic adenoma, mucinous cystic neoplasm, and lymphangioma.
Given the rarity of pancreatic cystosis, the need for surgical treatment is unclear. In one case, a patient with asymptomatic but palpable abdominal fullness from pancreatic cystosis was followed up for 1 year, with no morphologic or clinical change noted (95).
Pancreatic Abnormalities